Not sure about favorite brand but MSR and Katadyn are 2 reputable companies that make a wide variety of personal filters as well as larger filters suitable for a group. You might want to check out their web sites.
MSR seems to have better pricing on their stuff, but I know Katadyn to have a reputation for high end filters.
I have been meaning to pick one up myself as I am still in the dark ages filtering with a bandanna and either boiling off the nasties or using Aquaclear tablets. I don't mind doing it this way but a micro filter will be more efficient time-wise.